More consistently include config.h

src/common/plugin-timer.c

@@ -17,6 +17,8 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */
 
+#include "config.h"
+
 #include <stdlib.h>
 #include <string.h>
 #include <glib.h>